What's happening to my little tree?

Last summer, I got a Seven Sons Flowering tree. It's such a tiny thing really, but it's supposed to be a fast grower. Anyway, I planted in the ground and it did well all winter. About a month ago, I noticed my landscaper had nicked it with the gr trimmer, so I cut the nicked portion off, which was a good 5-6 inch branch. Wanting to avoid having that happen again, I dug it up and potted it until it could grow bigger and put it in a safe place in my garden where it still gets lots of sun. Then, a couple weeks later, I noticed another nick that I apparently overlooked the first time, so I trimmed the tree again just below the nick. Now, it's really really small, but it doesn't seem to be doing well. The leaves are wilting and it's not from lack of water. My mother told me her husband once nicked one of their tiny new trees and the tree ended up dying. I don't want that to happen! What could be the problem and is there anything I can do to save my little tree? Thanks!